1. Field of the Invention
The present invention relates to a furnace for heat treatment in vacuo, with cooling by a gas stream.
2. History of the Related Art
It is known that, in furnaces for heat treatment in vacuo comprising a heating enclosure in which is circulated a stream of gas cooled by a temperature exchanger surrounding the turbine which generates the stream, devices have already been provided for reversing the stream in an attempt to cool uniformly all the pieces constituting the charge.
For example, furnaces have already been proposed which are provided with an annular exchanger located downstream of the turbine generating the cooled gas stream and with channels for circulation of the stream provided with registers allowing the reversal of the direction thereof. The presence of the registers creates a flux which penetrates in the heating enclosure only via one of its sides and leaves via its opposite side. Under these conditions, only half of the exchanger is used for cooling the gas. Moreover, very considerable pressure drops occur around the registers and principally in the ring surrounding the turbine since the latter comprises only one output, the other being stopped by the register which is closed. Finally, if it is desired to reverse the direction of the flux by successive closure and opening of the registers, the flowrate of gas passes through a zero value on the charge. The drawbacks set forth above lead to overdimensioning of the motor for driving the turbine of which part of the power is transformed into heat which is completely lost. Finally, scavenging of the charge to be treated is not satisfactory since it is effected only by purely and simply reversing the stream of cooled gas.
Furnaces of the type in question have also been proposed, which present two opposite streams of the cooled gas so as to form eddies or opposing currents in the heating enclosure. There again, there are considerable pressure drops in the ring disposed around the turbine and around the flaps giving access to the channels for distributing the cooled gas, with the result that the power of the motor for driving the turbine must be provided to be greater than is necessary. As in the furnace mentioned hereinabove, the flowrate passes through a zero value, which is detrimental to correct heat treatment of the charge.